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The Onset of the Volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians): Eruption Chronology and Magma Type Variation

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The Onset of the Volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians): Eruption Chronology and Magma Type Variation Journal of Volcanology and Geothermal Research 354 (2018) 39–56 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores The onset of the volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians): Eruption chronology and magma type variation Kata Molnár a,⁎, Szabolcs Harangi a,b, Réka Lukács b,IstvánDunklc, Axel K. Schmitt d, Balázs Kiss b, Tamás Garamhegyi e,IoanSeghedif a Department of Petrology and Geochemistry, Eötvös Loránd University, Pázmány Péter stny. 1/c, H-1117 Budapest, Hungary b MTA-ELTE Volcanology Research Group, Budapest, Hungary c Sedimentology and Environmental Geology, Geoscience Centre, Georg-August University, Göttingen, Germany d Institute of Earth Sciences, Ruprecht-Karls University, Heidelberg, Germany e Department of Physical and Applied Geology, Eötvös Loránd University, Budapest, Hungary f Institute of Geodynamics, Romanian Academy, Bucharest, Romania article info abstract Article history: Combined zircon U-Th-Pb and (U-Th)/He dating was applied to refine the eruption chronology of the last 2 Myr Received 29 June 2017 for the andesitic and dacitic Pilişca volcano and Ciomadul Volcanic Dome Complex (CVDC), the youngest volcanic Received in revised form 9 January 2018 area of the Carpathian-Pannonian region, located in the southernmost Harghita, eastern-central Europe. The pro- Accepted 29 January 2018 posed eruption ages, which are supported also by the youngest zircon crystallization ages, are much younger Available online 3 February 2018 than the previously determined K/Ar ages. By dating every known eruption center in the CVDC, repose times be- Keywords: tween eruptive events were also accurately determined. Eruption of the andesite at Murgul Mare (1865 ± 87 ka) ş Zircon (U-Th)/He dating and dacite of the Pili ca volcanic complex (1640 ± 37 ka) terminated an earlier pulse of volcanic activity within Eruption chronology the southernmost Harghita region, west of the Olt valley. This was followed by the onset of the volcanism in the U-series dating CVDC, which occurred after several 100s kyr of eruptive quiescence. At ca. 1 Ma a significant change in the com- Quaternary position of erupted magma occurred from medium-K calc-alkaline compositions to high-K dacitic (Baba-Laposa Harghita dome at 942 ± 65 ka) and shoshonitic magmas (Malnaş and Bixad domes; 964 ± 46 ka and 907 ± 66 ka, respec- Carpathian-Pannonian region tively). Noteworthy, eruptions of magmas with distinct chemical compositions occurred within a restricted area, a few km from one another. These oldest lava domes of the CVDC form a NNE-SSW striking tectonic lineament along the Olt valley. Following a brief (ca. 100 kyr) hiatus, extrusion of high-K andesitic magma continued at Dealul Mare (842 ± 53 ka). After another ca. 200 kyr period of quiescence two high-K dacitic lava domes ex- truded (Puturosul: 642 ± 44 ka and Balvanyos: 583 ± 30 ka). The Turnul Apor lava extrusion occurred after a ca. 200 kyr repose time (at 344 ± 33 ka), whereas formation of the Haramul Mic lava dome (154 ± 16 ka) rep- resents the onset of the development of the prominent Ciomadul volcano. The accurate determination of erup- tion dates shows that the volcanic eruptions were often separated by prolonged (ca. 100 to 200 kyr) quiescence periods. Demonstration of recurrence of volcanism even after such long dormancy has to be consid- ered in assessing volcanic hazards, particularly in seemingly inactive volcanic areas, where no Holocene erup- tions occurred. The term of ‘volcanoes with Potentially Active Magma Storage’ illustrates the potential of volcanic rejuvenation for such long-dormant volcanoes with the existence of melt-bearing crustal magma body. © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction eruptions N10 kyr and possibly long repose times between active phases. Therefore, it is not easy to evaluate whether these volcanoes Constraining eruption chronology has a primary importance in can be reactivated after prolonged quiescence or have become extinct assessing volcanic hazards, since it provides information about the fre- (Connor et al., 2006). The poor knowledge about the nature of such quency of eruptions and the length of the repose time. Databases such long-dormant volcanoes is partly due to the difficulties to apply appro- as the Smithsonian's Global Volcanism Program collect available data priate geochronometers, which can be used to accurately determine the primarily for the Holocene volcanic activity (Siebert et al., 2011). On eruption ages for the last 1 Myr. the contrary, there is much less knowledge on volcanoes with known Over the last decade, combined application of U-Pb or U-Th and (U- Th)/He zircon geochronology has become a promising method to date ⁎ Corresponding author. volcanic eruptions occurring during the second half of Pleistocene E-mail address: [email protected] (K. Molnár). epoch (e.g., Schmitt et al., 2006, 2010; Danišík et al., 2012, 2017; https://doi.org/10.1016/j.jvolgeores.2018.01.025 0377-0273/© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 40 K. Molnár et al. / Journal of Volcanology and Geothermal Research 354 (2018) 39–56 Harangi et al., 2015a; Mucek et al., 2017). This technique is proved to be allows for an independent check of the accuracy of the dating. The erup- particularly applicable when other dating methods such as radiocarbon, tion ages were combined by newly analyzed major and trace element K/Ar or 40Ar/39Ar techniques encounter analytical or interpretational compositional data allowing the evaluation of chemical changes in the difficulties often caused by a lack of appropriate materials for dating erupted magmas. These data yield important new information about (Danišík et al., 2017). Rapid temperature decrease below the ~200 °C the nature of a little known long-dormant volcano in eastern-central closure temperature for He diffusion in zircon enables determination Europe. of eruption ages based on the (U-Th)/He systematics, assuming that no subsequent heating occurred (Farley, 2002). 2. Geological background The youngest volcanic activity of the Carpathian-Pannonian region occurred at Ciomadul volcano (Eastern Carpathians, Romania; Fig. 1). The Călimani-Gurghiu-Harghita volcanic chain (CGH) is located in Although, its youngest eruption is dated at ca. 30 ka (Vinkler et al., the southeastern part of the Carpathian-Pannonian region (CPR), 2007; Harangi et al., 2010, 2015a; Karátson et al., 2016) the composition eastern-central Europe (Fig. 1). The CPR comprises the Pannonian and flux of the emitted gases at mofettas (Vaselli et al., 2002; Kis et al., basin characterized by thin continental crust and lithosphere 2017), seismic tomography (Popa et al., 2012)aswellascombinedpet- surrounded by orogenic mountain belts of the Alps, Carpathians and rologic and magnetotelluric studies (Kiss et al., 2014; Harangi et al., Dinarides (e.g., Horváth et al., 2006). Major thinning of the lithosphere 2015b) indicate that there is still melt-bearing magma body beneath has been considered to be a result of the Early to Mid-Miocene the volcanic complex and therefore, there is still a potential for further retreating subduction of an oceanic lithosphere underneath at the East- volcanic activity at Ciomadul (Szakács et al., 2002; Harangi, 2007; ern Carpathians (e.g., Royden et al., 1983; Csontos et al., 1992; Horváth Szakács and Seghedi, 2013). Thus, there is a requirement for an accurate et al., 2006). The southeastern edge of the CGH is located ~50 km from knowledge on the eruption behavior of the volcanic system. The timing the Vrancea zone that exhibits the largest present-day strain concentra- of the last explosive eruptions and the chronology of the latest volcanic tion in continental Europe (Wenzel et al., 1999; Ismail-Zadeh et al., phase was determined by several authors (i.e., Moriya et al., 1995, 1996; 2012). This is due to a near-vertical slab descending into the upper man- Vinkler et al., 2007; Harangi et al., 2010, 2015a; Karátson et al., 2016). In tle (Oncescu et al., 1984; Martin et al., 2006) that poses a persistent re- this paper, we focus on the older history, i.e., the onset of the volcanism gional seismic hazard. The reason of the descending vertical lithospheric at the Ciomadul Volcanic Dome Complex (cf. Szakács et al., 2015), which slab beneath Vrancea is strongly debated. Explanations involve as it rep- comprises the volcanic edifice of Ciomadul and the peripheral lava resents the latest stage of the subduction along the Carpathians domes. Based on previous K/Ar ages (Peltz et al., 1987; Pécskay et al., (Sperner et al., 2001), but lithospheric delamination in the absence of 1995; Szakács et al., 2015) the peripheral domes are considered to subduction (Fillerup et al., 2010; Koulakov et al., 2010) or a combination have formed between 2 and 0.5 Ma. Here, we adopted the methodology of lithospheric delamination and subduction roll-back have been alter- used by Schmitt et al. (2006), Danišík et al. (2012) and Harangi et al. natively proposed (Gîrbacea and Frisch, 1998; Girbacea et al., 1998; (2015a), where they determined eruption ages from combined U-Th Chalot-Prat and Gîrbacea, 2000). and (U-Th)/He zircon dating. Individually, these chronometers yield in- Volcanic activity of the South Harghita and the nearby Perşani alkali dependent constraints on crystallization and eruption ages, but because basalt volcanic field could be related to this active tectonic setting, al- zircon crystallization always precedes eruption, the combined methods though the link between the vertical slab movement, magma Fig. 1. (A) Simplified geological map about the location of the Călimani-Gurghiu-Harghita volcanic chain in the Carpathian-Pannonian region (modified after Cloetingh et al., 2004 and Harangi et al., 2013).
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